Method of forming semiconductor devices containing metal cap layers

ABSTRACT

Embodiments of methods for improving electrical leakage performance and minimizing electromigration in semiconductor devices containing metal cap layers are generally described herein. According to one embodiment, a method of forming a semiconductor device includes planarizing a top surface of a workpiece to form a substantially planar surface with conductive paths and dielectric regions, forming metal cap layers on the conductive paths, and exposing the top surface of the workpiece to a dopant source from a gas cluster ion beam (GCIB) to form doped metal cap layers on the conductive paths and doped dielectric layers on the dielectric regions. According to some embodiments the metal cap layers and the doped metal cap layers contain a noble metal selected from Pt, Au, Ru, Rh, Ir, and Pd.

FIELD OF THE INVENTION

The invention relates generally to methods and processing systems forimproved dual damascene integration structures for semiconductorintegrated circuits.

BACKGROUND OF THE INVENTION

The semiconductor industry has had tremendous success in delivering evermore cost effective chips to market through the use of scaling. However,while scaling works well in device or front-end semiconductorprocessing, device wiring is not amenable to scaling and results indegraded interconnect resistance and/or capacitance. To alleviate thisproblem, the industry has been migrating to the use of a lowerresistance conductor, such as copper (Cu), and is also introducinglower-k (k=dielectric constant) insulators to reduce capacitance indamascene interconnect structures. Newly developed insulators in theultra-low-k (ULK) range (k<2.5) are generally characterized by a greatdeal of porosity (e.g., 30-50%). These materials are extremely fragileand difficult to integrate since they are susceptible to contaminationfrom other sources.

In a dual-damascene (DD) structure, a single metal deposition step isused to simultaneously form Cu metal lines and vias. The Cu metal linesand vias are formed by filling recessed features, such as a trench, avia, or other interconnect structure, in a dielectric film or substrate.After filling, the excess Cu metal that is deposited outside therecessed feature is removed by a chemical-mechanical polishing (CMP)process, thereby forming a planar structure with metal interconnectinlays.

The electrical current density in an integrated circuit's interconnectssignificantly increases for each successive technology node due todecreasing minimum feature sizes. Because electromigration (EM) andstress migration (SM) lifetimes are inversely proportional to currentdensity, EM and SM have fast become critical challenges. EM lifetime inCu dual damascene interconnect structures is strongly dependent onatomic Cu transport at the interfaces of bulk Cu metal and surroundingmaterials which is directly correlated to adhesion at these interfaces.New materials that provide better adhesion and better EM lifetime havebeen studied extensively. For example, a cobalt-tungsten-phosphorus(COWP) layer has been selectively deposited on bulk Cu metal using anelectroless plating technique. The interface of COWP and bulk Cu metalhas superior adhesion strength that yields longer EM lifetime. However,maintaining acceptable deposition selectivity on bulk Cu metal,especially for tight pitch Cu wiring, and maintaining good filmuniformity, has affected acceptance of this complex process.Furthermore, wet process steps using acidic solution may be detrimentalto the use of COWP.

SUMMARY OF THE INVENTION

The invention relates to a method of forming a semiconductor devicehaving doped metal cap layers on conductive paths and doped dielectriclayers on dielectric regions. To that end, the method includesplanarizing a top surface of a workpiece to form a substantially planarsurface with conductive paths and dielectric regions, forming metal caplayers on the conductive paths, and exposing the top surface of theworkpiece to a dopant source from a gas cluster ion beam (GCIB) to formthe doped metal cap layers on the conductive paths and the dopeddielectric layers on the dielectric regions. In one embodiment, themetal cap layers are selectively formed on the conductive paths relativeto the dielectric regions. In another embodiment, additional metal isformed on the dielectric regions. The additional metal may be at leastpartially removed by the exposure to the GCIB.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not as alimitation in the figures of the accompanying drawings.

FIG. 1 is a diagrammatic view of a gas cluster ion beam (GCIB)processing apparatus;

FIG. 2A is a cross-sectional view of a planarized workpiece illustratingconductive paths formed in recessed features;

FIG. 2B is an illustration of the workpiece in FIG. 2A after selectivelyforming metal cap layers on a planar surface of the conductive paths ofthe workpiece;

FIG. 2C is an illustration of the workpiece in FIG. 2B after treatingthe workpiece with a gas cluster ion beam (GCIB) to form doped layers;

FIG. 2D is an illustration of the workpiece in FIG. 2C after depositinga barrier layer over the workpiece;

FIG. 3A is a cross-sectional view of a planarized workpiece illustratingconductive paths formed in recessed features;

FIG. 3B is an illustration of the workpiece in FIG. 3A after formingmetal cap layers on a planar surface of the conductive paths of theworkpiece and forming metal on dielectric regions;

FIG. 3C is an illustration of the workpiece in FIG. 3B after treatingthe workpiece with a gas cluster ion beam (GCIB) to form doped layers;

FIG. 3D is an illustration of the workpiece in FIG. 3C after depositinga barrier layer over the workpiece;

FIG. 4 is a flowchart showing one embodiment of a method of modifying asubstantially planar surface of a workpiece with a GCIB; and

FIG. 5 is a flowchart showing another embodiment of a method ofmodifying a substantially planar surface of a workpiece with a GCIB.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS OF THE INVENTION

There is a general need for improving the reliability of devicescomprising copper and dielectric features, and in particular, conductivepaths and dielectric regions between the conductive paths exposed by aplanarization process. One way to improve reliability of devices is togetter metal impurities that may be present between conductive paths,resulting in an improved margin for line-to-line breakdown andelectrical leakage performance. Metal impurities may be gettered betweenconductive paths, such as Cu conductive paths, by exposing a surface toa doping source (e.g., a phosphorous (P)-containing source, a boron(B)-containing source, or a nitrogen (N)-containing source) using a gascluster ion beam (GCIB). Additionally, reliability may be improved byreducing electromigration of the conductive paths by incorporating adopant into metal cap layers over the conductive paths and into thedielectric regions and optionally also incorporating the dopant into theconductive paths, thereby minimizing a transport of conductive materialcaused by a momentum transfer between conducting electrons and diffusingmetal atoms.

Incorporating a dopant into the metal cap layers over the conductivepaths, optionally into the conductive paths, and into the dielectricregions between conductive paths exposed by a planarization processreduces electromigration and provides an improved margin forline-to-line breakdown and electrical leakage performance, resulting inimproved output parameters such as device or circuit characteristics.Some embodiments of the invention provide a method for integrating dopedmetal cap layers into Cu metallization of semiconductor devices toimprove electromigration (EM) and stress migration (SM) in the devices.According to some embodiments of the invention, the metal cap layers andthe doped metal cap layers contain a noble metal selected from platinum(Pt), gold (Au), ruthenium (Ru), rhodium (Rh), iridium (Ir), andpalladium (Pd).

With reference to FIG. 1, a GCIB processing apparatus 100 includes avacuum vessel 102 divided into three communicating chambers, a sourcechamber 104, an ionization/acceleration chamber 106, and a processingchamber 108. The chambers are evacuated to suitable operating pressuresby vacuum pumping systems 146 a, 146 b, and 146 c, respectively. Acondensable source gas 112 (for example argon or N₂) stored in a gasstorage cylinder 111 is admitted under pressure through gas meteringvalve 113 and gas feed tube 114 into stagnation chamber 116 and isejected into the substantially lower pressure vacuum through a properlyshaped nozzle 110. A supersonic gas jet 118 results. A condensablesource gas 112 may be a gas that condenses at temperatures greater than30 degrees Kelvin at one atmosphere, whereas a non-condensable sourcegas may be a gas that condenses at temperatures less than or equal to 30degrees Kelvin at one atmosphere. Suitable condensable source gases 112include, but are not necessarily limited to, phosphine (PH₃), diborane(B₂H₆), nitrogen trifluoride (NF₃), ammonia (NH₃), argon (Ar), nitrogen(N₂), carbon dioxide (CO₂), oxygen (O₂), and other gases and mixturesthereof. Suitable non-condensable source gases include, but are notnecessarily limited to helium (He), neon (Ne), hydrogen (H₂), andmixtures thereof.

Cooling, which results from the expansion in the jet, causes a portionof the gas jet 118 to condense into clusters, each comprising fromseveral to several thousand weakly bound atoms or molecules. A gasskimmer aperture 120 partially separates the gas molecules that have notcondensed into a cluster from the cluster jet so as to minimize pressurein the downstream regions where such higher pressures would bedetrimental (e.g., ionizer 122, high voltage electrodes 126, andprocessing chamber 108).

After the supersonic gas jet 118 containing gas-clusters has beenformed, the clusters are ionized in an ionizer 122. The ionizer 122 istypically an electron impact ionizer that produces thermoelectrons fromone or more incandescent filaments 124 and accelerates and directs theelectrons causing them to collide with the gas-clusters in the gas jet118, where the jet passes through the ionizer 122. The electron impactejects electrons from the clusters, causing a portion the clusters tobecome positively ionized. Some clusters may have more than one electronejected and may become multiply ionized. A set of suitably biased highvoltage electrodes 126 extracts the cluster ions from the ionizer,forming a beam, and then accelerates them to a desired energy (typicallywith acceleration potentials of from several hundred V to several tensof kV) and focuses them to form a GCIB 128. Filament power supply 136provides filament voltage V_(F) to heat the ionizer filament 124. Anodepower supply 134 provides anode voltage V_(A) to acceleratethermoelectrons emitted from filament 124 to cause them to irradiate thecluster-containing gas jet 118 to produce ions. Extraction power supply138 provides extraction voltage V_(E) to bias a high voltage electrodeto extract ions from the ionizing region of ionizer 122 and to form aGCIB 128. Accelerator power supply 140 provides acceleration voltageV_(Acc) to bias a high voltage electrode with respect to the ionizer 122so as to result in a total GCIB acceleration potential equal to V_(Acc).One or more lens power supplies (142 and 144 shown for example) may beprovided to bias high voltage electrodes with focusing voltages (V_(L1)and V_(L2) for example) to focus the GCIB 128.

A workpiece 152, which may be a semiconductor wafer or other workpieceto be processed by GCIB processing, is held on a workpiece holder 150,which can be disposed in the path of the GCIB 128. Since mostapplications contemplate the processing of large workpieces withspatially uniform results, a scanning system is desirable to uniformlyscan the GCIB 128 across large areas to produce spatially homogeneousresults.

The GCIB 128 is stationary, has a GCIB axis 129, and the workpiece 152is mechanically scanned through the GCIB 128 to distribute the effectsof the GCIB 128 over a surface of the workpiece 152.

An X-scan actuator 202 provides linear motion of the workpiece holder150 in the direction of X-scan motion 208 (into and out of the plane ofthe paper). A Y-scan actuator 204 provides linear motion of theworkpiece holder 150 in the direction of Y-scan motion 210, which istypically orthogonal to the X-scan motion 208. The combination ofX-scanning and Y-scanning motions moves the workpiece 152, held by theworkpiece holder 150, in a raster-like scanning motion through GCIB 128to cause a uniform (or otherwise programmed) irradiation of a surface ofthe workpiece 152 by the GCIB 128 for processing of the workpiece 152.The workpiece holder 150 disposes the workpiece 152 at an angle withrespect to the axis 129 of the GCIB 128 so that the GCIB 128 has anangle of beam incidence 206 with respect to the workpiece 152 surface.The angle of beam incidence 206 may be any suitable angle, but istypically 90 degrees or near 90 degrees. During Y-scanning, theworkpiece 152 and the workpiece holder 150 move from the position shownto the alternate position “A” indicated by the designators 152A and150A, respectively. Notice that in moving between the two positions, theworkpiece 152 is scanned through the GCIB 128 and in both extremepositions, is moved completely out of the path of the GCIB 128(over-scanned). Though not shown explicitly in FIG. 1, similar scanningand over-scan is performed in the (typically) orthogonal X-scan motion208 direction (in and out of the plane of the paper).

A beam current sensor 218 is disposed beyond the workpiece holder 150 inthe path of the GCIB 128 so as to intercept a sample of the GCIB 128when the workpiece holder 150 is scanned out of the path of the GCIB128. The beam current sensor 218 is typically a faraday cup or the like,closed except for a beam-entry opening, and is typically affixed to thewall of the vacuum vessel 102 with an electrically insulating mount 212.

A controller 220, which may be a microcomputer-based controller,connects to the X-scan actuator 202 and the Y-scan actuator 204 throughelectrical cable 216 and controls the X-scan actuator 202 and the Y-scanactuator 204 so as to place the workpiece 152 into or out of the GCIB128 and to scan the workpiece 152 uniformly relative to the GCIB 128 toachieve desired processing of the workpiece 152 by the GCIB 128.Controller 220 receives the sampled beam current collected by the beamcurrent sensor 218 by way of lead 214 and thereby monitors the GCIB andcontrols the GCIB dose received by the workpiece 152 by removing theworkpiece 152 from the GCIB 128 when a predetermined desired dose hasbeen delivered.

FIGS. 2A-2D depict, in schematic cross-section, one embodiment of themethod of the present invention. With reference to FIG. 2A and inaccordance with a representative embodiment, a cross-sectional view of aworkpiece 152 with a planarized top surface 230 illustrating conductivepaths 225 (e.g., Cu metal conductive paths) formed in recessed featuresis shown. A planarization process provides the planarized top surface230 to create a uniform surface while improving the optical resolutionof subsequent lithography steps. The planarization process may beterminated by detecting the presence of the top of dielectric regions235. The conductive paths 225 may be formed from a damascene process ora dual damascene process by etching a plurality of interconnect holes,known as vias, followed by a trench etch into the workpiece 152, apre-metal dielectric (PMD), or an inter-layer dielectric (ILD). Theworkpiece 152 may comprise silicon (Si), germanium (Ge), or a GroupIII-V semiconductor such as gallium arsenide (GaAs) or indium antimonide(InSb). A top layer of the workpiece 152 may be formed from an epitaxiallayer, a monocrystalline substrate or from a silicon-on-insulator (SOI)layer.

The series of interconnect holes and trenches formed through one or moreetching processes may be referred to as recessed features. The recessedfeatures are filled with a metal such as Cu using an electroplating or aphysical vapor deposition process (PVD), which is subsequentlyplanarized using a process such as chemical mechanical polishing (CMP),electropolishing, or ion milling to expose dielectric regions 235 andthe conductive paths 225 of the workpiece 152.

The conductive paths 225 may be lined with a barrier material 232 tolimit the amount of material transfer between the conductive paths 225and the dielectric regions 235. The barrier material 232 may be formedof one or more layers of tantalum, tantalum nitride, titanium, titaniumnitride, tungsten, and/or tungsten nitride. The barrier material may beformed using layering techniques including physical vapor deposition(PVD), atomic layer deposition (ALD), chemical vapor deposition (CVD),plasma enhanced chemical vapor deposition (PECVD), thermal deposition,and evaporation.

FIG. 2B is an illustration of the workpiece in FIG. 2A after selectivelyforming metal cap layers 270 on a planar surface of the conductive paths225 of the workpiece 152. According to some embodiments of theinvention, the metal cap layers 270 contain a noble metal selected fromPt, Au, Ru, Rh, Ir, and Pd. In one example, an average thickness of themetal cap layers 270 can be between 2 angstrom (angstrom=10⁻¹⁰ m) and100 angstrom, for example about 2, 5, 10, 15, 20, 30, 40, 50, 60, 70,80, 90, or 100 angstrom. However, embodiments of the invention are notlimited to those metal thicknesses and thicker metal cap layers 270 maybe formed and utilized.

The metal cap layers 270 are selectively formed on the conductive pathsrelative to the dielectric regions 235. The metal cap layers 270 may beformed using layering techniques including PVD, ALD, CVD, PECVD, thermaldeposition, and evaporation. According to one embodiment, ruthenium (Ru)metal cap layers 270 may be selectively deposited on the conductivepaths 225 relative to the dielectric regions 235 by a CVD process.Examples of selective Ru metal deposition processes are described inU.S. patent application Ser. Nos. 11/853,393 and 12/018,074. The entirecontents of these applications are incorporated herein by reference.

According to another embodiment, metal may be deposited on theconductive paths 225 and also on the dielectric regions 235 due to lossof selectivity during the metal deposition. Subsequently, metaldeposited on the dielectric regions 235 and a portion of the metaldeposited on the conductive paths 225 may be removed in a metal removalprocess to form the metal cap layers 270. Examples of Ru metaldeposition followed by a Ru metal removal process are described in U.S.patent application Ser. No. 12/173,814, filed on Jul. 15, 2008. Theentire content of this application is incorporated herein by reference.

FIG. 2C is an illustration of the workpiece 152 in FIG. 2B aftertreating the workpiece 152 with a dopant source 255 from a GCIB to formdoped dielectric layers 272, doped metal cap layers 276, and dopedconductive paths 274. According to some embodiments of the invention,the doped metal cap layers 276 contain a noble metal selected from Pt,Au, Ru, Rh, Ir, and Pd. The depth of the dopant incorporation into theworkpiece 152 may be controlled by the energy of the dopant atoms and/ordopant molecules in the dopant source 255. In one embodiment, a dopantis incorporated to a depth between 50 and 500 angstrom, or between 100and 200 angstrom. Although FIG. 2C depicts dopant incorporation into theconductive paths 225 to form the doped conductive paths 274, in otherembodiments of the invention, the energy of the dopant atoms and/ordopant molecules along with the thickness of the metal cap layers 270may be selected to substantially limit the dopant incorporation to themetal cap layers 270 and the dielectric regions 235 and not theconductive paths 225.

The dopant source 255 may be a stream of ionized gas clusters comprisinghundreds or thousands of dopant atoms and/or dopant-containingmolecules. Examples of dopants include phosphorus (P), boron (B), andnitrogen (N). Examples of dopant-containing molecules include PH₃, BH₃,B₂H₆, BF₃, NF₃, and NH₃. The dopant atoms and/or dopant molecules may beinfused into the dielectric regions 235, the metal cap layers 270, andoptionally the conductive paths 225 as described above. In one example,the dopant source 255 may be delivered by a GCIB to a dose from about5×10¹² atoms/cm² to about 1×10¹⁴ atoms/cm². The doped dielectric layer272, the doped metal cap layers 276, and optionally the doped conductivepaths 274, may contain between 0.1 and 10 atomic % of the dopant.

In one example, a phosphorus source 255 may comprise a single species,such as PH₃, or it may comprise a plurality of species including PH₃ anda non-condensable source gas, such as He, Ne, and/or H₂. In anotherexample, a boron source 255 may comprise a single species, such as B₂H₆,or it may comprise a plurality of species including B₂H₆ and anon-condensable source gas, such as He, Ne, and/or H₂. In yet anotherexample, a nitrogen source 255 may comprise a single species, such asNF₃, or it may comprise a plurality of species including NF₃ and anon-condensable source gas, such as He, Ne, and/or H₂.

GCIB processing has been shown to amorphize crystalline materials to adepth determined by the energy of the dopant atoms and/or dopantmolecules. The doped metal cap layers 276 may thus be at least partiallyamorphized by the dopant source 255 during the GCIB processing.Furthermore, in one example, phosphor doping of metal layers (e.g., Rumetal layers) has been shown to amorphize the metal layers and furtherinhibit metal grain growth during heat treatments following or duringthe GCIB processing. This effect can thus aid in inhibitingrecrystallization of the doped metal cap layers 276 and provide improvedCu barrier properties relative to undoped polycrystalline metal layersand other metal layers.

Following the dopant incorporation, the workpiece 152 may be annealedusing methods known to one skilled in the art to reduce any damagecreated by the dopant incorporation.

FIG. 2D is an illustration of the workpiece 152 in FIG. 2C after forminga barrier layer 250 over the doped metal cap layers 276 and the dopeddielectric layer 272. Although not shown in FIG. 2D, the barrier layer250 may getter any metal impurities between the conductive paths 225.The barrier layer 250 is deposited as a conformal layer using methodsknown to persons having ordinary skill in the art, such as CVD, PECVD,HDPCVD, MOCVD, ALD, PVD, or GCIB. The barrier layer 250 may comprisedielectric material such as silicon nitride or one or more barrier layermaterials such as silicon carbide, nitrogen doped silicon carbide,oxygen doped silicon carbide, boron carbon nitride, and boron nitride.

FIGS. 3A-3D depict, in schematic cross-section, another embodiment ofthe method of the present invention. FIG. 3A is a cross-sectional viewof a workpiece 153 identical to workpiece 152 in FIG. 2A, and containinga planarized top surface 230 illustrating conductive paths 225 formed inthe recessed features of dielectric regions 235.

FIG. 3B is an illustration of the workpiece in FIG. 3A after formingmetal cap layers 270 on a planar surface of the conductive paths of theworkpiece 153 and metal 278 on dielectric regions 235. The workpiece 153depicted in FIG. 3B is similar to the workpiece 152 depicted in FIG. 2Bbut also contains metal 278 on the dielectric regions 235 as a result ofloss of selectivity during metal deposition onto the workpiece 153depicted in FIG. 3A. According to some embodiments of the invention, themetal cap layers 270 and the metal 278 contain a noble metal selectedfrom Pt, Au, Ru, Rh, Ir, and Pd.

FIG. 3C is an illustration of the workpiece 153 in FIG. 3B aftertreating the workpiece 153 with dopant source 255 during GCIB processingto form doped dielectric layers 272, doped metal cap layers 276, anddoped conductive paths 274. According to some embodiments of theinvention, the doped metal cap layers 276 contain a noble metal selectedfrom Pt, Au, Ru, Rh, Ir, and Pd.

According to embodiments of the invention, the metal 278 and other metalimpurities between the conductive paths 225 may be partially removedfrom the dielectric regions 235 or completely removed from thedielectric regions 235 as depicted in FIG. 3C by the treating with thedopant source 255. Furthermore, although not shown in FIG. 3C, any metal278 remaining on the dielectric regions 235 after the treating may begettered by the dopants. According to one embodiment, the treating mayinclude simultaneous or sequential GCIB exposures of different dopantsources. In one example, the treating can include a first GCIB exposurecontaining NF₃, and a second GCIB exposure containing dopant-containingmolecules selected from PH₃, BH₃, B₂H₆, BF₃, and NH₃, for example. GCIBexposures containing NF₃ have been shown to effectively remove noblemetals such as Ru from surfaces. The depth of the dopant incorporationinto the workpiece 153 may be controlled by the energy of the dopantatoms and/or dopant molecules in the dopant source 255. In oneembodiment, a dopant is incorporated to a depth between 50 and 500angstrom, or between 100 and 200 angstrom. Although FIG. 3C depictsdopant incorporation into the conductive paths 225 to form the dopedconductive paths 274, in other embodiments, the energy of the dopantatoms and/or dopant molecules along with the thickness of the metal caplayers 270 may be selected to substantially limit the dopantincorporation to the metal cap layers 270 and the dielectric regions 235and not the conductive paths 225.

Following the dopant incorporation, the workpiece 153 may be annealedusing methods known to one skilled in the art to reduce any damagecreated by the dopant incorporation.

FIG. 3D is an illustration of the workpiece 153 in FIG. 3C afterdepositing a barrier layer 250 over the doped metal cap layers 276 andthe doped dielectric layer 272. The barrier layer 250 may further getterany remaining metal impurities between the conductive paths 225. Thebarrier layer 250 is deposited as a conformal layer using methods knownto persons having ordinary skill in the art, such as CVD, PECVD, HDPCVD,MOCVD, ALD, PVD, or GCIB. The barrier layer 250 may comprise dielectricmaterial such as silicon nitride or one or more barrier layer materialssuch as silicon carbide, nitrogen doped silicon carbide, oxygen dopedsilicon carbide, boron carbon nitride, and boron nitride.

Referring now to FIGS. 4 and 2A-2D, FIG. 4 is a flowchart showing oneembodiment of a method of modifying a substantially planar surface of aworkpiece 152 with a dopant source 255 during GCIB processing. Inelement 400, workpiece 152 is planarized to form a substantially planarsurface with conductive paths 225 (e.g., Cu metal conductive paths) anddielectric regions 235. In element 410, the planarized top surface 230is pre-treated to reduce or minimize contaminants from the planarizedtop surface 230. In one example, the pre-treatment may be a wet chemicalcleaning process to remove residual particles and material adsorbed onthe planarized top surface 230. The wet chemical clean process may use apost-CMP clean chemistry comprising de-ionized water, benzotriazine, andcitric acid or a solution particularly designed for post-CMP cleaningsuch as a ESC-700 series product manufactured by ATMI. In anotherexample, the pre-treatment may be an infusion etching step performed bya GCIB tool to treat or remove a portion of material from the planarizedtop surface 230. In another example, the pre-treatment may be asputtering step performed by a PVD tool to treat or remove a portion ofmaterial from the planarized top surface 230. While this embodimentincludes a pre-treatment, element 410 is optional.

In element 420, metal cap layers 270 are selectively formed on theconductive paths 225 of the workpiece 152. According to some embodimentsof the invention, the metal cap layers 270 contain a noble metalselected from Pt, Au, Ru, Rh, Ir, and Pd.

According to one embodiment, the metal cap layers 270 may be selectivelydeposited on the conductive paths 225 relative to the dielectric regions235. According to another embodiment, metal cap layers 270 may bedeposited on the conductive paths 225 and metal may be deposited on thedielectric regions 235 due to loss of selectivity during the metaldeposition. Subsequently, metal deposited on the dielectric regions 235and a portion of the metal deposited on the conductive paths 225 may beremoved in a metal removal process to selectively form the metal caplayers 270 on the conductive paths 225 relative to the dielectricregions 235.

In element 430, the planarized top surface 230 is treated with a dopantsource 255 to form doped dielectric layers 272, doped metal cap layers276, and optionally doped conductive paths 274, to getter metalcontaminants in the dielectric regions 235 and to minimizeelectromigration in the conductive paths 225. According to someembodiments of the invention, the doped metal cap layers 276 contain anoble metal selected from Pt, Au, Ru, Rh, Ir, and Pd. In element 440, abarrier layer 250 comprising a barrier material such as silicon nitride,silicon carbide, nitrogen doped silicon carbide, oxygen doped siliconcarbide, boron carbon nitride, and boron nitride is formed over thedoped layers 276 and 272. According to some embodiments, the barrierlayer may be formed by CVD, PECVD, HDPCVD, MOCVD, ALD, PVD, or GCIB. Inone example, a silicon nitride barrier layer 250 may be formed by a GCIBcontaining silane (SiH₄) and N₂. While this embodiment includes forminga barrier layer 250, element 430 is optional.

Referring now to FIGS. 5 and 3A-3D, FIG. 5 is a flowchart showing oneembodiment of a method of modifying a substantially planar surface of aworkpiece 153 with a dopant source 255 during GCIB processing. Inelement 500, a workpiece 153 is planarized to form a substantiallyplanar surface with conductive paths 225 and dielectric regions 235. Inelement 510, the planarized top surface 230 is pre-treated to reduce orminimize contaminants from the planarized top surface 230. Examples ofpre-treatments were described above in reference to FIG. 4. While thisembodiment includes a pre-treatment, element 510 is optional.

In element 520, metal cap layers 270 are deposited on the conductivepaths 225 and metal 278 is deposited on the dielectric regions 235 ofthe workpiece 153 due to loss of selectivity during the metaldeposition. According to some embodiments of the invention, the metalcap layers 270 and metal 278 contain a noble metal selected from Pt, Au,Ru, Rh, Ir, and Pd. In element 530, the planarized top surface 230 istreated with a dopant source 255 during GCIB processing to form dopeddielectric layers 272, doped metal cap layers 276, and optionally dopedconductive paths 274, to partially or completely remove the metal 278and other metal impurities in the dielectric regions 235 and to minimizeelectromigration in the conductive paths 225. According to someembodiments of the invention, the doped metal cap layers 276 contain anoble metal selected from Pt, Au, Ru, Rh, Ir, and Pd. In element 540, abarrier layer 250 comprising a barrier material such as silicon nitride,silicon carbide, nitrogen doped silicon carbide, oxygen doped siliconcarbide, boron carbon nitride, and boron nitride is formed over thedoped layers 276 and 272. According to some embodiments, the barrierlayer may be formed by CVD, PECVD, HDPCVD, MOCVD, ALD, PVD, or GCIB. Inone example, a silicon nitride barrier layer 250 may be formed by a GCIBcontaining silane (SiH₄) and N₂. While this embodiment includes forminga barrier layer 250, element 530 is optional.

A plurality of embodiments for methods to improve electrical leakageperformance and to minimize electromigration in semiconductor devicescontaining metal cap layers has been described. The foregoingdescription of the embodiments of the invention has been presented forthe purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed.This description and the claims following include terms, such as left,right, top, bottom, over, under, upper, lower, first, second, etc. thatare used for descriptive purposes only and are not to be construed aslimiting. For example, terms designating relative vertical positionrefer to a situation where a device side (or active surface) of asubstrate or upper layer is the “top” surface of that substrate; thesubstrate may actually be in any orientation so that a “top” side of asubstrate may be lower than the “bottom” side in a standard terrestrialframe of reference and still fall within the meaning of the term “top.”The term “on” as used herein (including in the claims) does not indicatethat a first layer “on” a second layer is directly on and in immediatecontact with the second layer unless such is specifically stated; theremay be a third layer or other structure between the first layer and thesecond layer on the first layer. The embodiments of a device or articledescribed herein can be manufactured, used, or shipped in a number ofpositions and orientations.

In the description and claims, the terms “coupled” and “connected,”along with their derivatives, are used. It should be understood thatthese terms are not intended as synonyms for each other. Rather, inparticular embodiments, “connected” may be used to indicate that two ormore elements are in direct physical or electrical contact with eachother while “coupled” may further mean that two or more elements are notin direct contact with each other, but yet still co-operate or interactwith each other.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, material, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention, but do not denote that theyare present in every embodiment. Thus, the appearances of the phrases“in one embodiment” or “in an embodiment” in various places throughoutthis specification are not necessarily referring to the same embodimentof the invention. Furthermore, the particular features, structures,materials, or characteristics may be combined in any suitable manner inone or more embodiments. Various additional layers and/or structures maybe included and/or described features may be omitted in otherembodiments.

Various operations will be described as multiple discrete operations inturn, in a manner that is most helpful in understanding the invention.However, the order of description should not be construed as to implythat these operations are necessarily order dependent. In particular,these operations need not be performed in the order of presentation.Operations described may be performed in a different order than thedescribed embodiment. Various additional operations may be performedand/or described operations may be omitted in additional embodiments.

Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the aboveteaching. Persons skilled in the art will recognize various equivalentcombinations and substitutions for various components shown in theFigures. It is therefore intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

1. A method of forming a semiconductor device, comprising: planarizing atop surface of a workpiece to form a substantially planar surface withconductive paths and dielectric regions; forming metal cap layers on theconductive paths; and exposing the top surface of the workpiece to adopant source from a gas cluster ion beam (GCIB) to introduce dopantsinto at least top portions of the metal cap layers and the dielectricregions to form doped metal cap layers on the conductive paths and dopeddielectric layers on the dielectric regions.
 2. The method of claim 1,wherein forming the metal cap layers comprises selectively forming metalcap layers on the conductive paths relative to the dielectric regions.3. The method of claim 1, wherein the metal cap layers and the dopedmetal cap layers contain a noble metal selected from Pt, Au, Ru, Rh, Ir,and Pd.
 4. The method of claim 1, wherein the dopant source comprisesdopants containing P, B, or N, or a combination thereof.
 5. The methodof claim 4, wherein the dopant source comprises a stream of ionized gasclusters of dopant-containing molecules selected from PH₃, BH₃, B₂H₆,BF₃, NF₃, and NH₃.
 6. The method of claim 4, wherein the doped metal caplayers and doped dielectric layers comprise between 0.1 atomic % and 10atomic % of the dopants.
 7. The method of claim 1, wherein the dopantsource further comprises a non-condensable source gas selected from He,Ne, or H₂, or a combination thereof.
 8. The method of claim 1, whereinthe exposing further forms doped conductive layers between the dopedmetal cap layers and the conductive paths.
 9. The method of claim 1,further comprising: forming a barrier layer over the doped metal caplayers and the doped dielectric layers.
 10. The method of claim 9,wherein the barrier layer comprises silicon nitride, silicon carbide,nitrogen doped silicon carbide, oxygen doped silicon carbide, boroncarbon nitride, or boron nitride.
 11. The method of claim 9, whereinforming the barrier layer comprises exposing the doped metal cap layersand doped dielectric layers to a gas cluster ion beam (GCIB).
 12. Themethod of claim 1, wherein forming the metal cap layers furthercomprises forming additional metal on the dielectric regions.
 13. Themethod of claim 12, wherein the exposing to a dopant source from GCIBremoves at least a portion of the additional metal from the dielectricregions.
 14. The method of claim 13, wherein the exposing comprisessimultaneous or sequential GCIB exposures of different dopant sources.15. A method of forming a semiconductor device, comprising: planarizinga top surface of a workpiece to form a substantially planar surface withconductive paths and dielectric regions; selectively forming metal caplayers on the conductive paths relative to the dielectric regions,wherein the metal cap layers contain a noble metal selected from Pt, Au,Ru, Rh, Ir, and Pd; and exposing the top surface of the workpiece to adopant source containing dopants selected from P, B, or N, or acombination thereof, from a gas cluster ion beam (GCIB) to introduce thedopants into at least top portions of the metal cap layers and thedielectric regions to form doped metal cap layers on the conductivepaths and doped dielectric layers on the dielectric regions, eachcomprising between 0.1 atomic % and 10 atomic % of the dopant.
 16. Themethod of claim 15, wherein the dopant source comprises a stream ofionized gas clusters of dopant-containing molecules selected from PH₃,BH₃, B₂H₆, BF₃, NF₃, and NH₃, and a non-condensable source gas selectedfrom He, Ne, or H₂, or a combination thereof.
 17. The method of claim15, wherein the exposing further forms doped conductive layers betweenthe doped metal cap layers and the conductive paths.
 18. The method ofclaim 15, further comprising: forming a barrier layer comprising siliconnitride, silicon carbide, nitrogen doped silicon carbide, oxygen dopedsilicon carbide, boron carbon nitride, or boron nitride over the dopedmetal cap layers and the doped dielectric layers by exposing the dopedmetal cap layers and doped dielectric layers to a GCIB.
 19. A method offorming a semiconductor device, comprising: planarizing a top surface ofa workpiece to form a substantially planar surface with conductive pathsand dielectric regions; forming metal cap layers on the conductive pathsand additional metal on the dielectric regions, wherein the metal caplayers and the additional metal contain a noble metal selected from Pt,Au, Ru, Rh, Ir, and Pd; and exposing the top surface of the workpiece toa dopant source containing dopants selected from P, B, or N, or acombination thereof, from a gas cluster ion beam (GCIB) to remove atleast a portion of the additional metal from the dielectric regions andto introduce the dopants into at least top portions of the metal caplayers and the dielectric regions to form doped metal cap layers on theconductive paths and doped dielectric layers on the dielectric regions,each comprising between 0.1 atomic % and 10 atomic % of the dopant. 20.The method of claim 19, wherein the dopant source comprises a stream ofionized gas clusters of dopant-containing molecules selected from PH₃,BH₃, B₂H₆, BF₃, NF₃, and NH₃, and a non-condensable source gas selectedfrom He, Ne, or H₂, or a combination thereof.
 21. The method of claim19, wherein the exposing further forms doped conductive layers betweenthe doped metal cap layers and the conductive paths.
 22. The method ofclaim 19, further comprising: forming a barrier layer comprising siliconnitride, silicon carbide, nitrogen doped silicon carbide, oxygen dopedsilicon carbide, boron carbon nitride, or boron nitride over the dopedmetal cap layers and the doped dielectric layers by exposing the dopedmetal cap layers and doped dielectric layers to a GCIB.
 23. The methodof claim 19, wherein the exposing comprises simultaneous or sequentialGCIB exposures of different dopant sources.